Amplification system



-w. A. MacDoNALD AMPLIFICATION SYSTEM Nqy. 18, 1930.

' Filed dot. 10, 1925 7a. .5 Mg MM ma m IW WW ,my ww a MA1 w m 4 w y m W l M, m M A, PW .IJ 1+ 111 l HHH Q f r ...HWI s G y @n @n x Wh Ef mw m1 m Nl m R w mu v it 1 P w www; w* Nbu VPatented Nev. 1s, 1930 UNITI-ED STATES lm'rala'rv oFFlc-r.

WILLIAM A. mcDoNALD, or LITTLE NEcx, NEW Yogur, AssIcNon 'ro IIAznL'rI'm:l coaroaA'rIoN, or JERSEY cI'rYZ, NEW JERSEY, A conoaa'rIoN or DELAWARE AMPLIFICATION SYSTEM Application filed October l0, 1925. Serial No. .$1,687.

This invention relates to amplifier systems,-

and, more particularly, to systems for the amplification of radio-frequency signals.

In the past, multistage 'radio-frequency am-A 5 plific'ation systems havebeen designed using coupling transformers of identical design lin each stage of amplification. Measurements and mathematical analyses indicate that the amplification in such systems is greatest in the shortest wave length, or highest frequency, and is only a fractional part of this value in the longest Wave length, or lowest frequency. As each stage has its maximum amplification at the same frequency, the addi- 1'5 tion of successive stages will accentuate this point of amplification in geometric ratio, with the result that when three or -more stages are employed the aggregate amplification is extremely high at one frequency and comparatively low at all others. Obviously this featur'e `is not desirable.

The present invention has for its object the provision of appropriate coupling means between the individual stages of a multistage tuned radio-frequency amplifier so that any desired ratio of maximum to minimum amplification may be obtained within the limits of the device.`

It has been recognized that in a multistage tuned radio-,frequency amplifier designed to opera-te over a wide wave length or frequency band, the amplification varieswith the'fref quency of tumngina manner dependent upon the specificconstruction of the coupling transformers. In former multistage tuned ampli- -fiers employing fixed values of inductance for both primary and secondary windings of theA interstage transformers, with variable coudensers as a means of tuning. thc construction of the transformers has been such-that the voltage developed across the terminals of .the secondary winding, and hence the amplification and relay action is a maximum when the smallest value of tuning condenser is used. This effect is due to the fact that when a capacit/31 is shunted across the terminals of the lsecondax'y'-wnding of an inter-' stagetransformer, and is varied so as to enaIthree-stage radio-frequency ampli catlon able the receiver in which it is'incorporated tion-frequency band. The present invention lv so that the envelope of the a gregate of ings,

to respond over a wide wave-length' or frequeney' range, the reactance of the secondary winding, and proportionately the voltage developed across it, will vary, fbothbeing a maximum when the smallest value of capacity is used, and a minimum when the largest lvalue of capacity is used.

The primary winding of the transformer which is included inthe output circuit of the precedingvacuum tube, is closely coupled' to the secondary winding thereof, and depends largely for the value of its impedance upon the impedance of the circuit in' Whichthe secondary winding is connected,with the result that when the impedance of thesecondary circuit varies with changes in the tuning capacltyf, the effective impedance of the primary circuit coupled thereto also varie's.

This inventlon takes advantage of the Wellknown principle that the maximum output of a vacuum tube is obtained vWhen the external or load impedance is substantially equal to the internal impedance of the tube. It follows that each stage of the radio-frequency amplifier, including its vacuum tube and transformer, will manifest a maximum relay action at that one frequency or wave-length which obtains when the internal -and output ycircuitimpedances are matched. For practical purposes a tunlngrange for each stage measured a certain distance each side of the so actual peak or point of maximum amplification frequency, will give satisfactory quant-itative amplification. This frequency band we may call the mean maximum amplificaprovides an arrangement of interstage transformers, each with its vacuum tube, having a different me'an maximum-frequency band, the ranges of these bands progressing successivethe bands will indicate substantia ly constant amplification over the desired frequency range ofthe receiver.

For a more complete understanding of the invention referencer-is made vto the drawv9:5

together with' the following description of a preferred embodiment, in which Fig. l discloses a radio receiver com rising system and a. detector; :m

Fig. 2 is a chart havin" curves showing the amplification effected by former radiofrequency amplifiers as compared with the radio-frequency amplifieiiof the present 1n vention;

- Fig. 3 shows a second cuart lndicating the amplification yeffected' by A they 'several stages of the radio-'frequency al'nplifieizfwhich in` the` aggregate produce avsubstantially straight line amplification, as indicated in the chart of Fig. 2j this figure also shows that with various coupling transformers the relay-action varies for difierentwave lengths or frequencies, and that it is impossible to obtain strictly the maximum relay .action -for vall frequencies within the desired band without a change in coupling between the several stages.

In Fig. 1 there is disclosed the circuit diagram of a threcsstage radio-frequency amplifier and detector combined in a radio receiving set, and provided with an antenna directly coupled to the tuned circuit including the inductance T1 and variable capacity C1 of the first stage 'of the amplifier, indicated by vacuumA tube V1. The output circuit of this tube is coupled to the tuned input circuit of a second stage of amplification, including` vacuum tube V2, by means of a radio-frequency transformer T2, In accordance with practice now Wellknown, a neutralizingr condenser Cm connects the grid circuit of vacuum tube V1 to an appropriate point on the secondary winding of transformer T3 to neutralize the undesirable capacity coupling of tube V1 and thereby to prevent all capacity reaction between the input circuit and the output circuitof this vacuum tube.y The output circuit of Vacuum tube V2, in the second 'stage of the amplifier, is coupled by means of a radio-frequency transformer1T3 to the ystuned input circuit of vacuum tube V3, of

the third radio-frequency stage. As in the case of the first radio-frequency stage, a neutralizing condenser, Cna connected to the grid circuitvof -vaeuum tube V2, and to an appropriate' poit on the secondary coil of transformer T3, likewise neutralizes any-capacity reaction effectsbetween the input circuit and the output circuit Aof the vacuum tube VJ., In like manner, the output circuit of vacuumtube V3, of thc third stage of amplification, is coupled by means of a radio-fr uency transformer T, to the input circuit of the detector, the vacuum tube of which is des,-

ignated V4'. A neutralizing condenser Cn, neutraliz'es ca acity reaction efects between t-he input an output circuits of the third radio stage.

i. In accordance the radio-frequen ransformers T2, T. and

wquency am lification, as indicated in Fig. 2,

iu which t e curve designated 2 indicates plifiers, the latter beine' 'th the present invention,

manna F'g. 1 and shows the improvement in amplification at the lowerfrequencies, as compared with present commercial radiofrequency amillustrated by /the curvedcsignated 1,in'Fig. 2.' i To effect this improved amplification, transformer T2 coupling the'first and second stages of the amplifier is selected so that it effects mean maximum amplification at a low wave length, as indicated by curve A, Fig. 3. To illustrate, if the internal impedance of tube V1 is 10,000

.ohms under given conditionsfthe maximum relay action will be obtained when the output circuit is also of 10,000 ohms impedance. The. primary winding of transformer Tgisltherefore so designed and coupled to the secondary winding that when condenser C2 is tuned to about 267 meters the input circuit of the transformer at resonance `willi have an effective im'- pedance of 10,000 ohms. Likewise, transforine1'T3, coupling thesecond and third vacuum tubes, V2 and V3', is designed to effect mean maximum amplification at an intermediate wave-length, as indicated by curve B, Fig.v 3, by designing the input circuit of the transformer to have an effective impedance of' 10,000 ohms when 'the secondary circuit is tuned to 400 meters; Likewise, transformer T4, coupling the output circuit of vacuum tube V3 to detector V4, is designed to effect its mean maximum amplification at a high wavelength, as indicated by curve C, because the input 'circuit at resonance will be of10,000 ohms effective impedance when the secondary circuit is tuned to about 533 meters. The aggregate and resultant amplification of the three transformers and their associated vacuum tube circuits, is shown by the curve designated 2, in Fig. 2, which indicates nearly straight-line amplification from 200 to 000 meters the entire range of the receiver. Transformers T2, T3 and T4, as well as coil T1, arepreferably varranged in such a manner as to eliminate undesirable electromagnetic coupling between them, whereby improved amplification will be realized. A

' The'invention may beA explained from another point of view as follows.

as 400 meters, the first stage transformer is ofless effective input impedance at resonance (the frequency of tuning) than that of the output circuit of the vacuum tube to which it .is connected; the effective input impedance The interl .stage transformers are designed so that at an intermediate wave-length, such, for example,

.tained becausel there is less dielectric loss and greater amplification in the first stage on short wave-lengths when'the effective input 400 meters is greater'than the output circuit impedance of t-he vacuum .tube in that stage.

The second stage transformer would in this l case be designed to have characteristics similar to the second stage transformer in the firstmentioned arrangement, namely, the effective input impedance at resonance ofthe transformer at 400 meters would be equal to the output circuitimpedance of the vacuum tube in that stage.

I claim:

1. In a mult-stage tuned radio-frequency vacuum tube amplifier, each stage vbeing coupled to the next adjacent stage by a single transformer', a variable condenser associated with each transformer in a tuned circuit for tuning the same over apredetermined wavelength range, the effective input impedance of each transformer at resonance being adj usted to such'value that .the ultimate amplification of all of said stages is substantially constant throughout said wave-length range' when all ofsaid condensers are adjusted so that their respective tuned circuitsare substantially in resonance with each other.

'2.v In a multi-stage tuned radio-frequency vacuum tube amplifier, each stage being coupled tothe next adjacent stage by a single transformer, a variable condenser associated with each transformer in a tuned circuit for tuning the same over a predetermined wave- 7length range, the effective input impedance of each transformer at resonance being adjusted' to such value that the ultimate amplification -of all of said stages is substantially constant throughout said wave-length range whenl all of said condensers are adjusted so that their respective tuned circuits are substantially in resonance :with each other, and means for eliminating undesirable elec-tromagnetic coupling betweenv the secondary windings of the. several interstage transformers whereby improved. amplification may be realized. f

3. In a multistage tuned radio-frequency vacuum tube amplifier,4 each stage being coupled tothe next adjacent stage by a singlev transformer, a variable 'condenser associated with each transformerin a tuned circuit'for tuning the same over a predetermlned Wavelength range, the e ective input impedance of each transformer at resonance being adjusted to such value that the ultimate amplification of all of said stages is substantially constant throughout said wave-leng-th range when all of said condensers are adjusted so that the tuned circuits in which said condensers are respectively'connected are substantially in resonance with each other, means for eliminating undesirable electro- .magneticy coupling vbetween the secondaryl windings'of the several interstage transformers, and means including a Winding of an interstage transformer for neutralizing undesirable capacity coupling in atleast one of said stages whereby increased amplification -may be realized.

4. lIn a multi-stage tuned radio-frequency vacuum tube amplifier, each stage being coupled to the next adjacent stage by a single transformer, a variable condenser assciated with each transformer in a tuned circuit for tuning the same over a predetermined Wavelength range, the effective input impedance at resonance of one of said transformers over a certain frequency range being less Athan the'output impedance of the tube in whose output circuit the primary winding of said transformer is connected, another of said transformers having over the same frequency transformer, .a variable condenser associated w1th each transformer 1n a tuned circuit for a certain frequency range being less-than` the output impedance of the vacuum tubein lwhoseoutput circuit the primary Winding of said transformer is connected, a second one of said transforme-rs having over the same frequency range an effective input impedance at resonance which is substantially equal to ythe output impedance of that vacuum tube in whose output circuit'the primary Winding of sald second transformer is connected, and a third one of said transformers havingover Athe same frequency range' an effective input impedance at resonance which 1s greater than the output impedance of the vacuum tube in' whose output circuit the primary winding of said third transformer is connected.

6. In an amplifier, a plurality of tuned amplifying stages,V each stage including a lvacuum tube, and means 'fora tuning lsaid stage to a plurality of narrow frequency' bands Within a relatively 'Wi-de frequency range, said means,Y including a transformer serving to couple the output ci'rcuitof one vacuum tube tq the input circuit of a succeedmg vacuum tube, the effective input impedanceat resonance of one of said trans` formers over a certain frequency range bel in whose output circuit said second transf ing substantially equal to the output impedance of the vacuum tube in whose output circuit said transformer is connected, a second ofsaid transformers having over a second Afrequency range an effective input impedance at resonance which is `substantially equal to the output impedance of the vacuum tube formerl is connected, and a third of said transformers having over a third frequency range an effective input impedance at resonance which is substantially equal to the output impedance of the vacuum tube in whose output circuit said third transformer is connected.

7. In an amplifier, a plurality of tuned amplifying stages, each stage including al vacuum tube, and means for tuning said stage to a plurality of narrow frequency bands Within a relatively wide frequency range, said means including a transformer serving to couple the output circuit of one vacuum tube to the input circuit of a succeeding vacuum tube, the effective input impedance at resonance of one of said transformers over a certain frequency range being substantially equal to the output impedance of the vacuum -tube in Whose output circuit said transformer is connected, a second of said transformers having over another frequency range an effecti-ve inputimpedance atresonance which is. substantially equal to the output impedance of the vacuum tube in whose output circuit said second-mentioned transformer is con- 8. In an amplifier, a plurality of amplifyingC stages, each stage including a vacuum tube, a plurality of transformers each serving to couple the output circuit of one vacuum tube to the input circuit of another vacnum tube of said amplifier, and means for tuning each transformer continuously over a predetermined frequency band, the value of the impedance of the primary circuit ofeacli transformer being a function of the impedance of the secondary circuit thereof, the impedance of said primary circuit at a certain mean maximum amplification Afrequency being substantially equal to the internal impedance of the tube in that stage, the impedance of theprimary circuit of another stage at a meanmaxiniuin amplification frequency different froin that of said first-mentioned stage tuning the' samev over fr redetermined wavelength range, `,the effective input impedance at resonance-of one of said transformers over a certain frequency range being-,less than the output impedance of the tube in whose output circuit the primary winding of said transformer is connected, another of said transformers having over the same frequency range an effective input impedance at resonance whichis greater than the output impedance of the vacuum tube in whose output circuit the primary winding of said other transformer is connected.

10. In a tuned radio-frequency receiver, a plurality of vacuum tubes coupled by radiofrequency transformers in cascade relation, each transformer having a tuned circuit and means for tuning said circuit over a certain frequency range, the effective input impedance of each transformer at resonance being adjusted to such value that the resultant amplification of all of said stages is nearly constant throughout said frequency range when all of said tuned circuits are adjusted so as to be substantially in resonance with each other.

11. In a multi-stage tuned radio-frequency amplifier,.the.method of amplifying radio signals which comprises tuning said-stages to resonance with the frequency of said signals, `selectively amplifying said signals -to a-different degree in each stage at the saine given frequency within a relatively Awide frequency range, and amplifying saidV signals in any given stage of said amplifier to a different degree at different frequencies within sai'd range, whereby the degreeof amplification of .said multistage amplifier is substantiallly uniform throughout the tuning range thereof. y

12. The combination in a high-frequency amplifying system tunable throughout a specified frequency range, of a plurality of thermionic tubes arranged in Cascade, each tube having an input section andan output Section, means coupling the output section of each said tube to the input section of a succeeding tube, one said coupling means including but a single transformer, said transformer having the characteristic that it is most efficient in transferring energy at the vlower frequencies of said frequency range,

and -a different said coupling means including but a single transformer, said transformi er having the characteristic that it is most efficient in transferring energy at the higher frequencies of said frequency range..

13. The combination in a. tuned high-frequency amplifying system effective throughout a specified frequency range, of a plurality of 1vacuum tubes arranged in cascade, means coupling an output circuit of-each said tube to a tunable input circuit of the succeeding tube,'

one said coupling means including but a -single transformer, said transformer having the characteristic that it is most efficient in transferring'energy.- at the lower frequencies of said frequency range, and a different said coupling means including' but a single transiao former, said last Vnamed transformer having- I the characteristic that it is most efficient in cuit of. one of 'said tubes, and a second transformer connected in the output circuit of another of said tubes, said transformers bein so arranged that the primary circuits thereo have different impedance lcharacteristics whereby one said transformer is most eiiic'ient in transferring energy at the lower frequencies of said frequency range, and the other of said transformer is most efficient in transferring energy at the higher frequencies of said frequency range.

In testimony whereof I aix my signature.

WILLIAM A. MACDONALD.

former connecte in the output circuit of 'another of said tubes, said transformer having ythe characteristic that it is most eicient intransferring energy at the higher frequencies of said frequenc range.

15..The combination in a tuned highfre` quency amplifying system effective throughout a specified range of frequencies, of a plurality of thermionic tubes arranged in cascade, each having an output circuit coupled to a tunable input circuit of the succeeding tube, a single transformer connected in the` output circuit of one of said tubes, said transformer havin the characteristic that it is most efficient 1n transferring energy at the lower frequencies of `said frequency range, and a single transformer connected to the output circuit of another of said tubes, said is most eiiicient intransferring energy at the higher frequencies of said frequency range, said transformers being so related that the overall amplification of the system is substantially constant throughout saidfrequency range. f v

16. The combination in a tuned high-frequencamplifier effective throughout a specified requency range comprisin a plurality of cascaded vacuum tube stages o the type including means suppressing Vthe effects of ca'- vpacitive coupling between control grid and plate, each tube'having'anoutput'circuit coupled to a tunable input circuit of the succeed-- ing tube,-of a single transformer connected lin lthe output circuit of one said tube, saidtransformer having the characteristic that it is most eicient in transferring energy at the' l,

lower frequencies of said frequency range, and a single transformer connected in the. output circuit of another of said tubes, saidtransformer having the characteristic that it is'most eicien't in. transferring energy at the V'ralityofvacuumtubes Aeachhaving higher frequencies of said frequency range. 17. The combination in atuned lil'lghefreuenc amplifying' system e ective oughdut a, y ed range of frequencies, of a pluarranged in e,

an output circuit coupled toa zilgzblen" cimltofasucedingtube, a.

transformer -having the characteristic that it ics Aism" viat 

